- Agronomic: general hay and forage crops, hay
- Animal Production: feed/forage
- Education and Training: extension, on-farm/ranch research
- Pest Management: biological control, field monitoring/scouting, integrated pest management
The goal of this research was to understand how insecticides impact natural enemy phenology and life stage structure, and how changes in these factors this might influence secondary pest suppression. Specifically, we used field surveys in insecticide treated and untreated alfalfa fields, laboratory feeding trials, and an outdoor cage experiment to assess how multiple enemy life stages and species diversity contribute to pea aphid suppression, a common secondary pest in alfalfa. Results from our survey show that phenological patterns of some natural enemy groups (e.g. big eyed bugs) allow them to temporally escape the most deleterious effects of early-season insecticide use, while others with early season phenology (e.g. damsel bugs) were impacted to a greater extent when early generations were removed by insecticides. Pea aphid abundance was found to not be significantly different between treated and untreated fields. In addition, surveys reveal a dynamic natural enemy community that fluctuates in both species and life stage composition across the growing season. Immature life stages were, at times, equally or more abundant than adult life stages, yet little is known how the presence of these multiple stages affect biological control outcomes. A cage experiment with treatments controlling for species richness and number of life stages reveals that the presence of multiple life stages increases pest suppression. Feeding trials indicate that different predator life stages consume different sizes of prey items, suggesting one possible mechanism through which multiple life stages can facilitate complimentary pest suppression when together. Ultimately, researching the dynamics of predatory insect communities can lead to pest management strategies that enhance the roles of natural pest suppression and minimize the impacts of pesticides. This research will contribute to our growing knowledge of biodiversity and ecosystem functioning for the benefit of managed agricultural settings, especially as it relates to Integrated Pest Management (IPM) strategies and the reduction of pesticides.
Alfalfa is an important crop to Utah agriculture, with nearly 50% of farms in Utah producing alfalfa hay in amounts exceeding 2 million tons per year (National Agricultural Statistics Service, 2014). Broad-spectrum insecticides are a major component of pest management in alfalfa, particularly for the control of alfalfa weevil. However, applications of broad spectrum insecticides have been implicated in creating conditions that favor secondary pest outbreaks, namely aphids in alfalfa (Evans 1993). Natural enemies mitigate the impacts of pest outbreaks, but the use of broad-spectrum insecticides remove or reduce densities of these predacious insects (Croft and Brown 1975). The resulting lack of predation pressure allow secondary pests to quickly multiply, potentially requiring additional pesticide use for their control (Settle et al. 1996). A focus on pest monitoring and the judicious use of insecticides using economic thresholds has aided in conservation biological control efforts that aim to protect natural enemies; however, adoption of these practices in Utah alfalfa production are not widespread. Although it is recognized that natural enemies provide valuable pest suppression services, there is relatively little information how insecticides impact phenology and the presence of multiple natural enemy life stages in alfalfa. It is also unknown how the presence of multiple enemy life stages impact pest suppression services. This project was aimed at understanding these components of the natural enemy community in an effort to aid conservation biological control efforts and integrated pest management strategies by providing greater knowledge about the natural enemy community, their impacts on aphid suppression, and how this might be influenced by insecticide use.
Natural enemy communities may be composed of many species, but they can also be composed of many life stages. Considerable evidence indicates that significant functional differences can exist between age groups of a single species (Wollrab et al. 2013; Polis 1984). This can be especially pronounced in insects since the process of complete and incomplete metamorphosis yield discreet physiological differences between adult and immature insects. Insect traits such as size, mobility, or even form can completely change over the course of ontogenetic development. Evidence suggests that diverse communities of natural enemies can improve pest suppression (Letourneau et al. 2009; Hooper et al. 2005; Cardinale et al. 2006). This is often attributed to complementary interactions between organisms where diverse communities utilize resources more efficiently than less diverse communities (Losey and Denno 1998). This can be enabled through mechanisms such as resource partitioning, where functional trait differences (e.g. foraging techniques, prey preferences, mobility, diel patterns) enable the division of resources (e.g., food, habitat, mates) across multiple organisms in space and time (Finke and Snyder 2008). The presence of multiple life stages may be a source of functional diversity that can influence biological control activities beyond the species richness level.
Generally, natural enemy diversity research has represented diversity at the species richness level with enemies in the adult life stage. However, both life-stage structure and species composition of the natural enemy community can dynamically change throughout a growing season according to species’ phenological patterns. Integrating multiple life stages into diversity research can more adequately reflect the natural community. Pest suppression services may also be limited by natural enemy phenology and the disturbances which might affect phenological patterns, such as insecticide use. If early season insecticide applications for alfalfa weevil have negative effects on natural enemy phenology or life stage structure, it could disrupt the biological control of aphids or other secondary pest insects later in the season. This project was targeted at investigating aspects of the natural enemy community that contribute to pest suppression with an emphasis on how this relates to predator phenology and life stage dynamics. Ultimately, this can be used to advance the integration of ecologically-based pest management to minimize the impacts of pesticides on the natural enemy community.
Cardinale, B. J., et al. (2006). “Effects of biodiversity on the functioning of trophic groups and ecosystems.” Nature 443(7114): 989-992.
Croft, B. and A. Brown (1975). “Responses of arthropod natural enemies to insecticides.” Annual Review of Entomology 20(1): 285-335.
Elvin, M. K. and P. E. Sloderbeck (1984). “A key to nymphs of selected species of Nabidae (Hemiptera) in the Southeastern USA.” The Florida Entomologist 67(2): 269-273.
Evans, E. W., Karren, J., Hurst, C. (1993). “Pea aphid outbreaks associated with spraying for the alfalfa weevil in Utah.” Utah State University Cooperative Extension Fact Sheet No. 85.
Finke, D. L. and W. E. Snyder (2008). “Niche partitioning increases resource exploitation by diverse communities.” Science 321(5895): 1488-1490.
Hooper, D. U., et al. (2005). “Effects of biodiversity on ecosystem functioning: a consensus of current knowledge.” Ecological Monographs 75(1): 3-35.
Letourneau, D. K., et al. (2009). “Effects of natural enemy biodiversity on the suppression of arthropod herbivores in terrestrial ecosystems.” Annual Review of Ecology, Evolution, and Systematics 40(1): 573-592.
Losey, J. E. and R. F. Denno (1998). “Positive predator–predator interactions: enhanced predation rates and synergistic suppression of aphid populations.” Ecology 79(6): 2143-2152.
Polis, G. A. (1984). “Age structure component of niche width and intraspecific resource partitioning: can age groups function as ecological species?” The American Naturalist 123(4): 541-564.
Settle, W. H., et al. (1996). “Managing tropical rice pests through conservation of generalist natural enemies and alternative prey.” Ecology 77(7): 1975-1988.
Snyder, W. E. and A. R. Ives (2001). “Generalist predators disrupt biological control by a specialist parasitoid.” Ecology 82(3): 705-716.
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Wollrab, S., et al. (2013). “Ontogenetic diet shifts promote predator-mediated coexistence.” Ecology 94(12): 2886-2897.
Project objectives:div style="margin-left:1em;">
Alfalfa harbors a diverse community of generalist natural enemies, including damsel bugs, big-eyed bugs, and lady beetles that contribute to the control of aphids (Snyder and Ives 2001), yet little is known about how dynamic communities of adult and juvenile predators interact to suppress pests throughout a growing season and how this might be affected by insecticide applications. The objectives of this research were to:
1) Quantify alfalfa yield, pest, and beneficial insect species and life stages present in commercial alfalfa fields treated and untreated for alfalfa weevil,
2) determine the feeding differences between adults and juveniles of four common insect predators found in alfalfa, and
3) determine the impact of multiple predator life-stages in diverse predator communities on prey suppression and yield.